1. Field of the Invention
The present invention relates to navigation systems particularly for automated vehicles which move in accordance with programmed control without the use of guidance wires or tracks.
2. Description of Related Art
Navigation control for automated vehicles systems are described in GA-A-2 143 395 and GB-A-2 158 965. In the system of GA-A-2 158 965 the path of the vehicle is determined by a dead reckoning system which calculates the linear and angular movement of the vehicle during a short time interval from the angle of rotation and the steering angle of a guidance wheel, for example a castor wheel, on the vehicle. In this way the system predicts its own position at any time. The position so predicted by the dead reckoning system is checked at intervals by taking a bearing to a retro-reflector of known position using a scanning laser source on the vehicle. The positional error, detected by means of such a bearing operation, is then used to correct the position information by means of a filter.
This system suffers certain disadvantages, because of inherent errors in the measurement of the linear distance and angle through which the vehicle has moved within each time interval. These errors arise as a result of variations in the castor wheel radius caused, for example, by wear, inaccuracies in the measurement of the steering angle of the castor wheel during each time interval, and because the vehicle may tend to move with a "crabbing" motion.